In general, a brake disc of a vehicle refers to a device used for decelerating or stopping the vehicle, and configures an essential braking system of the vehicle. The brake disc used in the braking system converts kinetic energy of the vehicle to heat energy and the like by using frictional force generated through friction with a friction material to stop or decelerating the vehicle.
In a brake disc in the related art, all of a hat part mounted to a hub and a friction part rubbed during braking are manufactured from a single material such as gray cast iron having a flake graphite structure to exhibit excellent braking characteristics, such as vibration damping performance, a damping property, a heat radiating property, and a lubricating function.
Recently, vehicle industries have devoted to development of technologies for improving fuel efficiency in accordance with depletion of petroleum energy, a climatic change issue and an increase in greenhouse gas. Among those efforts, a technology for reducing a weight of a vehicle without deteriorating the performance of the vehicle has been focused for improving fuel efficiency.
Particularly, reducing in weight in a lower part of the vehicle may directly influence performance and fuel efficiency of the vehicle, and a decrease in unstrung mass, which is directly related to a wheel driving load, may be efficient to improve fuel efficiency.
For example, in order to reduce the weight of the brake disc in the lower part of the vehicle, a brake disc manufactured from heterogeneous materials, in which the friction part adopts gray cast iron and the hat part adopts aluminum, has been developed.
However, when the brake disc made of the heterogeneous materials has a condition in which a braking speed and a braking load are severe, such as in the case where a temperature of a friction surface is increased to about 800° C., a crack 30 may be generated in the friction part due to a difference in a thermal expansion coefficient between a friction part 10 made of gray cast iron and a hat part 20 made of an aluminum alloy (FIG. 1).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.